Chillers comprising an evaporator and a condenser have long been known. Typically, the condenser and evaporator will each comprise heat exchangers that have many smaller tubes that pass through a larger tube, or shell. Also typically, a refrigerant having a suitably low specific heat and vapor pressure, such as a fluorocarbon, sold under the trademark Freon, is passed through the shell while a heat exchanging liquid having a relatively high specific heat and vapor pressure, such as water, is passed through the smaller tubes. So passing through the heat exchanger, heat is transferred between the refrigerant and the heat exchanging liquid.
In the evaporator, heat is extracted from the heat exchanging liquid as the refrigerant is heated and, thus, gasified. The resulting cold heat exchanging liquid is routed for air conditioning, industrial cooling, and the like. The resulting gasified refrigerant is routed to a compressor where it is compressed to increase its pressure. From the compressor, the pressurized refrigerant is routed to the condenser. In the condenser, the pressurized refrigerant gas is passed through the shell of the heat exchanger having smaller tubes through which a cooling heat exchanging liquid is passed. So passing through the heat exchanger, the refrigerant is cooled and the heat exchanging liquid is heated.
At the increased pressure of the condenser and the lower temperature, the refrigerant changes phase from gas back to liquid. The liquefied refrigerant is routed back to the evaporator through a pressure valve. As the pressure is lowered, the refrigerant becomes again cold. The cold, liquid refrigerant is again used to cool the heat exchanging liquid in the evaporator, and the cycle is repeated.
One of the major problems with chillers of the above kind is that leaks develop in the heat exchangers. Such leaks typically arise from internal and external corrosion and cracking, which is caused by the high pressures, extreme temperatures, and the caustic nature of the refrigerants and heat exchanging liquids. Leaks are very undesirable, because they decrease the efficiency of the chillers and cause wasting of refrigerant. Furthermore, the refrigerant used in chillers is typically Freon, the release of which into the environment is now known to cause damage to the Earth's ozone layer. As the dangers of leaking Freon have been discovered, it has become increasingly important to monitor and to prevent such leakage.
Detecting Freon leaks in chillers is not practicable using the prior art. Such leaks are usually small, and the Freon is discreetly carried from the chiller by the heat exchanging fluid that exits the heat exchangers.
U.S. Pat. No. 4,910,463 to Williams discloses an apparatus for detecting levels of halogen gases, such as Freon, in a confined space. Upon detecting a pre-determined concentration of halogen gas, the apparatus can sound an alarm. The apparatus is not capable of continuously detecting refrigerant in the flow of a heat exchanging liquid such as water.
U.S. Pat. No. 4,862,698 to Morgan et al. discloses a method and apparatus to detect refrigerant leaks by increasing the temperature of the refrigerant, thereby increasing the refrigerant pressure and making it easier to detect refrigerant leaks. This method is not applicable to the typical chiller refrigeration system because raising the refrigerant temperature would adversely affect the performance of the chiller while it is on-line. This method would work only if the chiller system is off-line and the refrigerant temperature is stabilized. In addition, this invention does not address a method for detecting the existence of refrigerant in the heat exchange fluid.
U.S. Pat. No. 5,228,304 to Ryan discloses a method and apparatus for determining the amount of refrigerant in a closed system by monitoring the liquid refrigerant level in the system utilizing a float apparatus. This is not applicable to monitoring the refrigerant levels in chiller refrigerant systems because the liquid refrigerant levels in chiller systems fluctuate drastically depending on the heat load on the heat exchanger. This method does not address a direct method for detecting the existence of refrigerant in the heat exchange fluid.
None of the foregoing prior art teaches how to test for refrigerant in a flow of heat exchanging fluid, such as water, in a chiller.